Nested clade phylogeographical analysis of the finless porpoise (Neophocaena phocaenoides) inhabiting Chinese and Japanese coasts.

The finless porpoise (Neophocaena phocaenoides) is a small cetacean whose survival is largely affected by human activity. The characteristics and structures of 3 populations in China and 4 to 5 populations in Japan have been well documented, although their history and origins remain poorly understood. In this study, nested clade phylogeographical analysis was applied to mtDNA sequences from finless porpoises to delineate the historical factors shaping the divergence pattern of this species. The sampling range covered most habitats of the finless porpoise, including the Chinese and Japanese coasts and the Yangtze River. A nested cladogram was constructed, and all 3 (2-step) clades were linked together without interior or tip status. Our data indicated that haplotype C was the most common among most individuals and populations, which could be the most ancient haplotype among all of the sampled types. As populations expanded to reside in different areas, ancient types with haplotype C mutated to other haplotypes, which were kept endemic by geological barriers that changed during glacial cycles that retarded gene flow. Populations in Japanese Pacific coasts and inland sea and post-arc marginal seacoasts and the Yangtze River were formed by the residual individuals left when allopatric fragmentation occurred in the ancestral population. The existence of highly endemic haplotypes and high genetic diversity from the Ariake Sound, Tachibana Bay, and the Yellow Sea indicated a relatively isolated state in these areas during the evolutionary history of the finless porpoise. The phylogenetic pattern revealed in the present study provided a better understanding of the biogeographical events that affected the finless porpoise within this region.